Past research has shown that stressful events can alter neuroendocrine and immune functioning, and may be associated with increased susceptibility to certain diseases. In an effort to more fully understand these relationships, researchers have sought to identify the cognitive and affective mediators that intervene between the stressful situation and biological and health outcomes, as well as individual difference factors thought to modify stress reactivity. This proposal is concerned with the role of a particular psychological domain, that of the self, in individuals' responses to stressful events. Specifically, the proposed program of research will examine self-evaluative threat as a mediator of stress-induced changes in endocrine (cortisol) and immune (macrophage) parameters. In addition, the role of an individual difference factor, that of trait self- esteem, will be examined as a moderator of these processes. To chance the ability to examine self evaluative processes in stress reactions, individuals' responses to stressful performance situations will be studied, in which success and failure performance will be manipulated in the context of an experimental stressor, and measured during a naturalistic stressor, that of taking the Graduate Record Exam. Success and failure is expected to elicit different patterns of self-evaluation (positive v. negative), which result in differing cognitive self-appraisal and self-specific affective responses, and subsequent changes in cortisol, and macrophage immune activity. Trait self-esteem is also expected to moderate these processes. This program of research will more early define the role of the self in individuals' biological reactions to common experimental and naturalistic stressors.